Process of and apparatus for cooling electrical generators



April 26, 1960 1.. HELLER ETAL 2,934,655

PROCESS OF AND APPARATUS FOR COOLING ELECTRICAL GENERATQRS Filed. DEC. 15. 1958 2 Sheets-Sheet 1 mvmrons MA H- \\E\.L2R- RRPAV 5mm BY I April 26, 1960 7 L.v HELLER ET AL ,9 5

PROCBSSOF M9 APPARA-Tus 'FCR cootms ELECTRICAL GENERATORS Filed Dec. 15, 1958 2 Shams-sheet 2 INVENTORS msno MZLLXirk APQP D mm A assesses I sending value, and its secondary function is to maintain this set value by the appropriate switching in of the cooling equipment.

-(2) Since as long as the temperature of the cooling gas does not exceed the set value, the system operates only with natural cooling, i.c., with the fresh cooling water passing either through the auxiliary cooling device or through both parts of the main heat exchanger, the control system must change the cooling operation from natural to artificial cooling whenever the temperature reaches the said set value.

(3.) The output of the artificial cooling and the temperatures of the circulating condensate, respectively, have to be so set as to obtain a cooling gas temperature which at its maximum corresponds to the set value,

(4) With respect to the system employing both a main and an auxiliary heat exchanger, care must be taken that simultaneously with the switching in of artificial cooling, the fresh cooling water is diverted so as to bypass the auxiliary heat exchanger prior to its entry into the main heat exchanger. correspondingly, with respect to the system employing only a main heat exchanger the "cold" part of which is adapted to be traversed by both fresh water and condensate, care must be taken that simultaneously with the switching of artificial cooling, the fresh cooling water is blocked off from the "cold" part of the heat exchanger and is permitted to flow only into the -hOt part of the heat exchanger.

(5) Care has to be taken that, during artificial cooling, the circulating condensate should pass into the sprayers of the evaporator, while during natural cooling it should be led into the evaporator at a point below the liquid level therein. This is necessary because, during artificial cooling, the returning warmed up condensate must flow through the nozzles in order to achieve the evaporation needed for the recooling or, in other words, to obtainthe requisite augmented evaporating surface needed for it, whereas during natural cooling the vaporization of the condensate, returning at unchanged temperature, would be a drawback since it would cause serious dilficulties in the setting of the ejector which serves for the deaeration of the evaporator. The ejector would suck in a part of the vaporized or atomized condensate, in the form of steam, since otherwise the atomized condensate would suck steam back into the evaporator and would thus practically operate as a condenser. If, however, according to the present invention, in case of natural cooling, the condensate is directed to enter the evaporator at a location close to the suction pipe of the circulating pump, below the liquid level in the evaporator and through a separate pipe, this ensures that there is no effect whatever on the conditions prevailing in the space above the liquid level of the evaporator, and the deaerating ejector may operate undisturbed and with a minimum quantity of steam.

(6) Care must also be taken that in the evaporator of the refrigerating machine there is maintained a pressure corresponding to the desired temperature conditions even during natural cooling.

The systems according to the present invention solve all these problems and enable these requirements to be met most simply and thus most economically. The varinus valves employed to direct the flow of the natural cooling water and condensate are so connected with their operating elements as to ensure in a simple manner the mutual forced shifting movements thereof, thereby eliminating the possibility of wrong operations.

The foregoing and other objects, advantages and characteristics of the present invention will become more fully clear from the following detailed description thereof when read in conjunction with the accompanying drawings, in which:

Fig. 1 is a diagrammatic and schematic illustration of a control system constructed in accordance with the principles of the present invention and adapted for use with a combined main and auxiliary heat exchanger type of generator cooling arrangement; and

Fig. 2 is a diagrammatic and schematic illustration of a modified type of control system adapted for use with a cooling arrangement in which only one heat exchanger is employed.

Referring first to Fig. l, a generator 26 (representative of a complete power station as explained in the abovemcnticned copending patent application) is there shown as being driven by a steam turbine 3 through the intermediary of suitable means 3a. A conduit 2, which may be provided with pump means for circulating the generator cooling medium (usually a gas, such as air, hydrogen or the like, although a liquid may also be used), is provided with an intermediate portion 2a disposed in a main heat exchanger 11 in which it is placed into heat exchange relationship with two coils or like conduits l2 and 15. These coils are in communication with the two coils 9a and 911, respectively, of an auxiliary heat exchanger 9, in which the natural. cooling water and the condensate maybe placed into heat exchange relationship with each other. A water feed conduit 25 communicates with the coil 9a, a three-way valve 6 being incorporated in the conduit to permit the water to be diverted, when desired, into a conduit 10 bypassing the coil 9a. Condensate is fed into the main heat exchanger coil 15 through a conduit 14 and from the evaporator 18 of a refrigerating ma chine by means of a pump 13 incorporated in the conduit 14. A three/way valve 7 controls the outlet of the auxilitary heat exchanger coil 9b and enables the condensate to be directed either into a conduit 16 communicating with the evaporator 18 at a point below the liquid level therein, or into a conduit 16a terminating in a pinrality of nozzles or sprayers 17 in the evaporator above the liquid level therein.

The turbine 3 is provided with a steam supply conduit 3b, in which is located a load controller or governor 4, and with two steam exhaust conduits 3c and 3d. The main exhaust conduit 30 communicates with a condenser 27 which in turn communicates with a return conduit 27:: the outlet end of which is located in the evaporator 18 and controlled by a float-operated, liquid level-responsive valve 27b. The auxiliary steam exhaust conduit 3d, by

means of which partlyused steam may be bled from the turbine 3, communicates via a valve 23 with a steam jet ejector 24 which deaerates the evaporator 18 to the condenser 27 of the turbine 3. The conduit 3d also communicates with a pair of conduits Se in each of which is arranged a valve 19 controlling the inlet to a respective steam jet ejector 20,- tbe outlets of which are in communication via check valves 22 with the condenser 27, and

the suction points of which are in communication via turbine. It will further be understood that all times only condensate flows through the coils 15 and 9b, and only fresh cooling water flows through the coils 9a and 12.

The operation of the structure so far described is fully set forth in the aforesaid copending application and may be summarized as follows:

When natural cooling is desired, the steamv jet ejectors 20 are-shut down to stop evaporative cooling of the condensate which is, therefore, merely circulated by the pump 13 into the coil 15 (the "cold" part of the main heat exchanger 11) and thence into the coil 9b of the auxiliary heat exchanger 9, where the warmed condensate transfers its accumulated heat to the still cold water inse to v2 the" g eneretor, and the third ,Of fihlchi .1

.. scsns hl f i-fl ss u r msissc st a m t; th re r ton sv riszit a sr osd.

'ticulal ed to Jhelever .;41' at opposite sides of the fulcrum 8 thereola,re' two linlt'nrms'li and 45.. 11 formerof which is connected tothef operating amide of the three 'fwny vulve IG, and "tholatter of which isconnccted to the ,opersi'tingjar'm "7a ot'the threeway velve 7. The valves asses flowing throufih the coil as, from which the partly warmed water enters the coil 12- (the "hot" part c! the its main heat exchanger truer extracting turth erheatfrom" the generator cooling medium; The condensate cooled in the coil 9!: is returned to the evaporator via conduit 16.

n the other hand, when artificial cooling is desired, the fresh water is admitted to the coil ll through the bypass conduit while the condensate, which thus cannot be cooled while flowing through the coil 81:, is returned to the evaporator via conduit lfiannd spray norzles 17, the e'j'ectorsf 201heing renderedoperative at this time means evaporation and consequent cooling of condensate. in the. evaporator. In orderto compensate for vapors removed from the evaporator-.18 by the electors ZlLcondensedstcam and 'vaporsarereturned to the evaporator, as needed, via-the conduit 27a.

,{Ihe actual control means provided, aocording to the present invention/for setting the reterence or nominal j temperature valueof the generatorcooling medium, i.e.,

the maximum tempcratnreto which thesaid medium rosy be'pepnltted tol rise before jar tificial cooling is'required and initiated, comprises plurality or temperaturedon the conduitor line .2} edjacenfthe cooling linsertedlin the line 2 adjacenttlie co gas inletof inscrtedin the iet oi -the g encrator zfl thececdnd of which is the operating valves 19, thcrchyrendering the steam jet 'ejectors 20 inoperative. At the same time, the device 5 is caused to shift the three-way valves 6 and 7 into their "natural cooling? positions topermit fresh water to flow into the coil 9a-of the auxiliary heat exchanger andto connect the outlet of the coil 9b of the auxiliary heat exchanger'to the-conduit 16. Asset forth hereinabove and in the aforesaid copending application, the condom sate will now be merely. circulatedby the pump 13 from the evaporator 18 through the conduit 14, coil/15, coil 91: and conduit 16 backlto the evaporator (in which 'no' cvaporstive cooling takes place). Any heat extracted by the condensate from the generator cooling gas in the col part 'offthe main-heat exchanger 11 will be dissipatedat coil 96 into the coldlwat'er flowing through coil 9a, which water, after so cooling the condensate, flows line 2 the sensing .lcleinent ,35jand lt hc, conduit 1 portionfza. Each of'these lfiempe'raturees'n sing elements an b fi ss' p adi s s ngsie hs' t n is urnsare adopted-"tofelfecipredeterrninedchanges of an associated electrical resistance. 'Thiefthrce resistances assoclsted-it ith"the' sensing elements 3510,37 are" conlnected in series with one'snother to ensure that the .t'otal'.rcsistnntx vhltie'rlses with eithcr'an increase of the 'ditferencehetween the temperature of the cooling gas attlie generator outlet and inletor with an incrcaseof the outlct'cooling gas t'ernpcratm:e.

I,.Thc series-connected resistances areconnected tonne Windingofa differential l rel ay' 1; aslndicated schematiis ll' a w t is hfl fl s -sl ser bifs dis as e o e greats of which, in responseto. variations in the fluid volthrough the. coil 12 ,to extract more heat from the generator cooling gas at the "hot"- side of the main heat exchanger. All the loss heat of thegenerator accumulated by the cooling gas is. thus, ultimately absorbed by the cooling water.

In the event that the maximum temperature of the cool- .ing gas rises to orahove thc set nominal value, the sum of the resistances associatedlwiththe temperature-sensing elements 35, 36 and 37 and connected to the first coll el tist: differential relay 1 .will'hecc'me greater than the adjusted fixed value of the variablelresistance connected with the second coil of the diflcrential relay 1, whereby the latter sends an impulse to the shifting device 5 to cause the same to switch the three-way valves 6 and 7. fittedinto the cooling water andcondcnsdte pipes or conduirs 25. and 14, respectively, over to their "artificial cooltially'hy' thejbr'ken line 8; the other ,windingol the In any. suitable dianniyadby electrical, mechanical or 'difierentialrelav being c"onnected-to a variable resistance.

fluid pressure trnnsn'tjslsion'fnieans, the difierential relay 1. ma? 'additionallir'he' rendered responslvetothe output of the gene ates-so as to erl'su'ne that theaforesaid norm? 1:

.nal tentpsfrature; or the cooling gasj corresponds .to such .b ilplll. {Byway'ofiexarnple, the releyfmfilt 1 f ing? 'wlththe load-. cQntr'oIIer, or governor-f4, as indifloated: schenjpticglly hyfilofifpkn 1ine39 Alternatively,

' on be st ed, b ew e;

o ours t {t e 8 3 m 5 ull lllo the", tsal relay mo mor s h s l y sermon lnterrnediatejt' ends at 8. "Ar- 6 and} 7 may, of course be designed for operation by the device Stlirohkh electrical or' fluld pressure means in lieu of the mechanical means. illustrated! The shiftingpulse, either mechanically, electt'icallyior by fluid pres- ':sure, as schematically indicated, bykth'e broken line A5,. to; them op rsfine-vsl cs ss ia d with me on jet ejector: 20 in the conduits 3e.

o the device articulated sa positions; Upon switching over r the three-way valves, whichls accompanied'by openingof the valves 1!? for thesteam jet ejectors zfl-hythe device Sviarncans 45, the cooling water. will not flow from pipe 25 to the -'hot part or coil -12 of the main heat exchanger-'11 through vcoll 9o ofthe auxiliary heat exchanger 9, being by valve 6 to now" through the bypass pipe or conduit 10. Thus, the condensateheing circulated hy the 13 and flowing lhrough the "cold" parrot coil 1520: the main hest exch'ang'egwill not be cooled in the auxiliary heat exchanger 9, but, due to the setting of the three-way.valve 'Lwillreach the evaporator lflthrough the conduit 16:: and; semen, 17, where itwill becooled by'e'vaporation resulting the" action of the ejector-s 20 as aided by the sprayersl or atoiniier nozzles "17..

Should the-n raximunlcooiing gas temperature new fall below the set value thereof, the sbove, described process will ,work' in reverse, beginning with the interruption of the sil'pply of working'stearri to the electors 2d and continning. with the resetting of thethree-way valves 6 and '7 into their original or natural cooling positions. The check valves 22, at this time, function to prevent ingressof steam into the evaporator from the, condenser, since in their absence the condenser 27, which is connected to the delivery pressure pipes of the ejectors 20,- would be in communication with the-evaporaeor. alt all times, of course, the evaporator 18 is decorated tothe condenser liyejectorzsw a 2 Referringnow to Fig.1; the control system there illustrsted, heingadaptodfor use with a generator cooling ar- .rsngernent in which, the provision of anauxiliarylheat ex! changer 'is-dis'pensed with,- diflerslsomewhstiroin that illustrated in 'Fig. 1. To as extent that the two control systems are identical, a repetition of the description of the control system partsis deemed unnecessary, and correspondingly some of these parts are not illustrated in Fig. 2 or, if illustrated, are designated by the same reference numerals employed in Fig. l.

The cooling arrangement itself difiers from that shown in Fig. l as follows. The water feed pipe or conduit 25 is connected to a three-way valve 34 adapted, when in one position, to direct the flow of water into a conduit 34a leading directly to the "hot" part or coil 12 of the heat exchanger 11, and adapted, when in another position, to direct the flow of water into a conduit 34b. The latter merges with a conduit 28 feeding into the "cold" part or coil 15 of the heat exchanger 11 from a threeway valve 31 to which condensate is fed by the pump 13 from the evaporator 18. The valve 31, in one of its positions, permits flow of condensate into the conduit 28, and in the other of its positions directs the flow of condensate into the return conduit 16 leading to the evaporator and entering the same at a point below the. liquid level therein. The outlet end of the coil 15 is connected to a conduit 28a leading to a three-way valve 29 which, in one of its positions, directs the condensate flow into the re turn conduit 16:: leading to the spraycrs or nozzles 17 in the evaporator, and in the other of its positions directs the condensate flow into a conduit 30 merging with the conduit 34a leading to the heat exchanger coil 12.

As can be readily seen, the control system of Fig. 2 difiers from that of Fig. l essentially only in the structure of the switching means for the three-way valves. The shifting device 5, which is adapted to be actuated by im pulses transmitted from the differential relay 1 (not shown in Fig. 2) by the means 40 and is likewise adapted to actuate the operating valves 19 via the means 45, is again provided with a movable member 41 articulated to one end of a lever 46 fulcrumed intermediate its ends at 8 and articulated at its other end to a link 47. The link 47 is in turn articulated at its other end to a rotatable drive plate 32 shaped as an internal gear having teeth 33. The valves 29, 31 and 34 are provided with operating pinions 29, 31' and 34, respectively, the teeth of which mesh with the teeth 33 of the gear 32.

In operation, for natural cooling the cooling water from conduit 25 passes through the three-way valve 34 which is set in such a way that the water flows into the conduit or pipe 28 and through it into the coil 15 of the heat exchanger 11. From this coil, the cooling water reaches the three-way valve 29 which is so set that the water will enter the conduit 30 and flow into the coil .12 of the heat exchanger 11. At the same, time, the threeway valve 31 is so set that the condensate being circulated by the pump 13 flows from conduit 14 through the return pipe or conduit 16 into the evaporator 18. It will,

therefore, be understood that with this arrangement the entire cooling is eflected by the natural cooling water which, by this series-connection of the heat exchanger coils 15 and 12 passes first through the former and then through the latter, thereby dissipating the entire quantity of the loss heat. The valves'19 are closed at this stage, rendering the refrigerating machine inoperative.

When, due to a rise in the maximum cooling gas temperature in the conduit 2 to a value above the preset or nominal value, the difi'erential relay sends to the device the impulse required for initiating the artificial cooling, the device 5, through the intermediary oi the moving mechanism 46-47, rotates the gear 32 which, by means of the pinions 29', 31 and 34', will switch over all three three-way valves simultaneously. The principle of mechanical moving is, of course, mentioned here only by way of example, as any other type of system, |.e., hydraulic, pneumatic or electrical, may be adopted.

After the change-over, the natural cooling water flows through the three-way valve 34 into the conduit 34:: and through this into the hot part or coil 12 ot the heat exchanger 11. At the same time, with conduit 34b closed by valve 34, the three-way valve 31, directs the flow of cold condensate into conduit 28 and thence to the cold" part or coil 15 of the heat exchanger 11, while the threeway valve 29 blocks the way leading to pipe 30 and leads the condensate which has just passed through the "cold part or coil 15 of the heat exchanger into conduit 16a and to the sprayer-s 17 of the evaporator. Concurrently, the valves 19 were opened by the shifting device 5 to render evaporative cooling of the heated condensate possible.

Due to the fact that the circulating pump 13 keeps the condensate in constant circulation, regardless of the position of the valve 31, the switching over from natural to artificial cooling or vice versa still calls for only one single operation, i.e., for the moving of the switching gear mechanism 32.

it will be appreciated that the mechanical switching arrangements 4142-43-44 etc. and 41-4647-32 etc, both of which may be replaced by electrical or fluid pressureeoperated means, enable the process of the present invention, to wit the controlling of the cooling of the generator cooling medium, to be carried out simply and efiiciently in direct response to the operational conditions or loading of the generator.

To illustrate the specific manner in which the principles of the present invention are put into practice, the following example may be considered. It is well known, in conformity 'with generally accepted practice, that a modern generator is constructed for operation at a given maximum permissible temperature. It, now, such a generator is to be operated at a still higher output, in accordance with one of the expressed objects of the invention, a greater amount of loss heat will have to be dissipated, which will require a greater difference between the temperatures of the generator parts on the one hand and the cooling medium on the other hand. Since, by virtue of the construction of the generator, it is impossible, within the limits of optimum operational efliciency, to raise the temperature of its parts, the only manner in which the required greater temperature difference can be attained is by lowering the temperature of the cooling medium, as previously set forth herein. Stated in other words, since the dissipation of a greater amount of loss heat will produce a greater temperature rise in the gaseous cooling medium, it is necessary to lower the inlet temperature thereof to such an extent that even with the greater temperature rise there is maintained a suflicient dilference between the maximum or outlet temperature of the cooling medium and the rated maximum operating temperature of the generator parts.

By way of example, let it be assumed that a generator is to be operated at a temperature of C. and that the cooling medium initially enters the generator at a temperature of 30 C. and leaves it at a temperature of 60 C. Thus, the minimum diflerence between the generator operating temperature and the maximum cooling medium temperature is 20', while the temperature rise of the cooling medium during its passage through the generator is equal to 30.

Should the load increase to such an extent that a loss of hcatexceeding the normal amount by 33% must be dissipated in the generator, the minimum temperature difi'erence between the generator and the cooling medium must be increased by 33% or 6.6, yielding an ultimate difference of 26.6. However, at the same time the temperature rise of the cooling medium will be increased by 33%, i.e., from 30 to 40. Consequently, since the outlet temperature of the cooling medium will be 53.4 C., the inlet temperature of the cooling medium will have to be 13.4 C.

It will be readily seen that the needed lowering of the cooling medium temperatures is eiiected by the switching in of the artificial cooling arrangement, as described hereinabove, whenever the cooling medium temperature a 7 ass-nose at the outlet of the generator exceeds a preset nominal value. 7

Although there have been described herein preferred embodiments of the present invention, it is understood that this disclosure is tor the purpose of illustration only and that various omissions and changes in shape, proportion and arrangement of the parts, as well as the substitution of equivalent elements for thearrangements shown and described, may be made without departing from the scope of the invention as set forth in' the appended claims.

Having this described the invention, what is claimed and sought to be protected by Letters Patent is:

l. The process of controlling the cooling of a cooling medium circulated through an electrical generator, com prising the steps of predetermininga nominal value for the outlet temperature of said cooling medium, sensing at least said outlet temperature, subjecting said cooling medium to a naturalvcooling operation as long as said sensed outlet temperature does not exceed said nominal value thereof, and subjecting said cooling medium to a combined natural and artificial cooling operation when said sensed outlet temperature exceeds said nominal value thereof.

2. The process of controlling, by means of natural cooling water and a refrigerating machine of the steam jet compressor type, the cooling of a cooling medium circulated through an electrical generator, comprising the steps of setting a nominal value for the temperature ofsaid cooling medium in correspondence with the operating load of said generator, subjecting said cooling medium efiectively only to the cooling action of said natural water upon 'said temperature being lower than said nominal value thereof, and subjecting said cooling medium to the joint cooling action of said natural cooling. water and said refrigerating machine upon said tern perature being higher than said nominal value thereof.

3. Apparatus for controlling the cooling of an electrical generator cooling medium by means of natural cooling water and the condensate of a steam jet compressor refrigerating machine equipped with steam jet ejector means and. operating valve means for opening and closing the steam flow path to said elector means,-

comprising means for sensing the temperature of said cooling medium, a load-responsive control memher connected with said sensing means for setting a corresponding nominal value for said temperature, three-way valve means controlling the. flow of said natural cooling water and said condensate into heat exchange relationship with said cooling medium, said three-way valve means being operable when in a first position thereof to direct said 'ilow. ofwater and condensate so as to' render the water the only efiecfivecooling agent, and further operable when in a second position thereof todirect said flow of water and condensate so as to render both of the same effective cooling agents, and switching means operatively connected to said operating valve means and to said three-way valve means and respousiveto the output of said control member in response to signals from said sensing means for either closing said operating valve means to render said ejector means inoperative and si-v multaneously switching said three-way valve means into said first position thereof, or opening said operating valve means to render said ejector means operative and simultaneously switching said three-way valve means into said second position thereof, in accordance, respectively, with a decrease or an increase of said load. 1

4. Apparatus according to claim 3, wherein said generator is driven by a steam turbine, further comprising a load governor regulating the input or steam into said turbine, and means operatively interconnecting said con trol member with said load governor.

5. Apparatus according to claim 3, said sensing means comprising a plurality of temperatme-responsive elemeats arranged at the cooling medium inlet and outlet 75 valve means being dperablawhen in said first position locations of said generator, and means dlflerentially connectlng said sensing means to said control member for actuation of the latterln response to the difierence'between theinlet and outlet temperatures of said cooling medium f 6. Apparatus according to. claim 3, said three-way valve means comprising a plurality of three-way valves, each of said three-way valves being provided with an operating piniomrsaidswitching means comprising gear means meshing with said pinion: for simultaneous operation of all of said three-way valves.

7. Apparatus according to claim 3, said three-way valve means comprising a plurality of three-way valves, each of said three-way valves being provided with an operating arm, said switching means comprising linkage means operatively connected to said operating arms for simultaneous operation of all of said three-way valves.

8. Apparatus for cooling an electrical generator driven by a steam. turbine having a condenser for exhaust steam, comprising i means for circulating a cooling medium through said generator, a heat exchanger 'for extracting loss heat from said cooling medium, at least first and second coils in heat exchange relationship sequentially with the initial and final sections oithe path of flow of said cooling medium through said heat exchanger, evaporator means containing refrigerant condensate connected with said second coil, pump'means for circulating said condensate from and back to said evaporator, first steam jet ejector means connected to said evaporator and operable by partly used exhaustedsteam from said turbine to eliect evaporation of condensate in said evaporator and to force some of the resultant vapors into said condenser, operating valve means controlling the steam inlet to said first ejector means and adapted, when open, to render the same operative'and, whenclosed, to render the same inoperative, check valve means operatively con- ,nected between the outlet of said first ejector means and said condenser for inhibiting return flow of steam from said condenser into said first ejector means, second steam jet ejector means'operablc by partly used exhaust steam from said turbine for decorating said evaporator to said condenser, means for circulating natural cooling water at least throughsaid first coil, three-way valve means controlling the how of, saidwater and condensate, shifting means operatively connected to said three-way valve means for switching the same to either a first position or a second position so as to render said three way valve means operable to direct such flow to said heat exchanger in a manner corresponding to natural cooling or artificial cooling, respectively, said shifting means being further operatively connected to said operating valve means for closing the same when switching said three-way valve means to said first position and for opening said operating valve means when switching said three-way valve means to said second position thereof, and control means .operatively connected with said shifting means and responsive to load conditions of said generator for substantially jointly actuating said three-way valve means and said operating valve means intothe natural cooling or artificial cooling states thereot in accordance with corresponding .load variations tending to produce lesser or greater temperature rises in said cooling medium during its passage thro g said generator.

9. Apparatus according to claim 8. said three-way valve means being operable, when in said firstposition thereof, to serially connect-said second and first coils for flow of said cooling water through both said coils, while causing said condensate to bypass said-second'coil and be returned to raid. evaporator, said three way valve means being operable, when in said second position thereof, to direct the flow of cooling water only into said first coil while directing the dew of'condensate only into said second coil and thence back to said evaporator.

10. Apparatus according to claim .8, said three-way second call for return entry into said evaporator at a thereof, to direct said cooling water to said first coil and cooling water to said first coil out of heat exchange resaid condensate through said second coil and into heat lationship with said condensate leaving said second coil.

exchange relationship with said cooling water prior to arrival of the latter at said first coil, and to thereafter References cited m the file of am Patent direct said condensate for return entry into said evapora- 5 UNITED STATES PATENTS tor at a point below the liquid level ther in, sai hr 1,390,062 Smith Sept. 6, 1921 wfly valve means being operable, when in said second 1,74 5 5 Baumann 13% 31' 1929 positron thereof, to direct said condensate through sald FOREIGN PATENTS point above the liquid level therein, and to direct said 10 79,317 Germany June 23, I933 

